Malaysian police have threatened to arrest those participating in an unsanctioned rally to protest results of an election the opposition says was marred by massive fraud.

National police chief Ismail Omar says the protest to be held late Wednesday is illegal because the organizer, outspoken opposition leader Anwar Ibrahim, did not apply for a government permit.

Malaysia's Peaceful Assembly Act tightly regulates protests and public gatherings, and requires organizers to receive advance permission for rallies. Anwar, an ex-deputy prime minister, has said the law is an undemocratic assault on free speech.

Anwar has encouraged Malaysians to wear black to the protest, which will be held at a sports stadium in Kuala Lumpur. He says it is the beginning of a "fierce movement" to challenge the vote and reform Malaysia's electoral system.

Final results from the Sunday vote show the long-ruling National Front coalition captured a large majority of the seats, despite losing the popular vote to Anwar's Pakatan Rakyat coalition.

Numerous rumors of cheating plagued the polls, including the use of ink to mark voters that critics say could be easily washed off. There also were complaints of foreigners being flown into the country to cast ballots.

Prime Minister Najib Razak, who was sworn in on Monday, has firmly dismissed the charges, insisting that the results were in line with opinion polls that suggested his coalition was likely to win.

Although the ruling bloc was able to win 133 of the 222 available seats and extend its 56-year rule, it only received 48 percent of the popular vote, compared to 52 percent for the opposition. It is the coalition's poorest electoral performance since independence from Britain in 1957.